Organic EL display provided with gel-state encapsulant incorporating a desiccant and a high molecular-weight medium

ABSTRACT

A sealing substrate is arranged to oppositely face an element substrate or which organic EL layers are formed in a matrix array with a sealing material sandwiched therebetween. A gel-state desiccant is filled in an inner space surrounded by the element substrate, the sealing substrate and the sealing material. Since the gel-state desiccant is in a gel state, the gel-state desiccant is flexibly filled in the inner space of the organic EL display device thus completely eliminating a gap. Since the inner space is filled with the gel-state desiccant, moisture hardly intrudes into the inner space from the outside and, at the same time, a mechanical strength of the organic EL display device is also enhanced.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation of U.S. application Ser. No.13/067,967 filed Jul. 12, 2011, which is a Divisional of U.S.application Ser. No. 12/382,224 filed Mar. 11, 2009. Priority is claimedbased on U.S. application Ser. No. 13/067,967 filed Jul. 12, 2011, whichclaims priority from U.S. application Ser. No. 12/382,224 filed Mar. 11,2009, which claims priority from Japanese application JP2008-89996 filedon Mar. 31, 2008, the content of which is hereby incorporated byreference into this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an organic EL display device, andmore-particularly to an organic EL display device which preventsdeterioration of an organic EL layer due to moisture and exhibitsexcellent life characteristics.

2. Background Art

In an organic EL display device, an organic EL layer is sandwichedbetween a pixel electrode (lower electrode) and an upper electrode, afixed voltage is applied to the upper electrode, and emission of lightfrom the organic EL layer is controlled by applying a data signalvoltage to the lower electrode thus forming an image. The data signalvoltage is supplied to the lower electrode via a thin film transistor(TFT).

An organic EL display device is classified into a bottom-emission-typeorganic EL display device in which light emitted from organic EL layersis taken out in the direction of a glass substrate on which the organicEL layers and the like are formed and a top-emission-type organic ELdisplay device in which light emitted from organic EL layers is takenout in the direction opposite to a glass substrate on which the organicEL layers and the like are formed. The top-emission-type organic ELdisplay device has an advantage that the respective organic EL layerscan ensure a large light emission area thus increasing the brightness ofa display.

When moisture is present in an organic EL material used in an organic ELdisplay device, the light emission characteristic is deteriorated andhence, when the organic EL display device is operated for a long time,portions of the organic EL material which are deteriorated with moisturedo not emit light. These portions appear as dark spots on a displayregion. The dark spots grow with time and become a defect of an image.

To prevent the generation or the growth of the dark spots, it isnecessary to prevent the intrusion of moisture into the organic ELdisplay device or to remove the intruded moisture from the organic ELdisplay device. Accordingly, an element substrate on which an organic ELlayer is formed is sealed by a sealing substrate thus preventing theintrusion of moisture into the inside of the organic EL display devicefrom the outside. On the other hand, to remove moisture intruded intothe inside of the organic EL display device, a desiccant is arranged inthe inside of the organic EL display device. This organic EL displaydevice is referred to as a hollow-sealed-type organic EL display device.

The hollow-sealed-type organic EL display device has drawbacks such asdifficulty in adjusting a gap between the element substrate and thesealing substrate and difficulty in adjusting pressure in a sealed spaceinside the organic EL display device. For example, the sealing materialis made of an ultra violet-ray curing epoxy resin. This resin cannotcompletely interrupt the intrusion of moisture from the outside andhence, the intruded moisture is diffused in a hollow portion.Accordingly, it is difficult to effectively protect an organic EL layerfrom moisture in case of the hollow-sealed-type organic EL displaydevice.

To cope with such drawbacks attributed to the hollow sealed structure,there has been known a solid sealing technique which is disclosed inJP-A-2004-157517 (patent document 1). The solid sealing technique is atechnique in which a space defined between an element substrate and asealing substrate is filled with a liquid or a solid body such as anadhesive material. Patent document 1 discloses the constitution in whichthe element substrate and the sealing substrate which has a recessedportion are laminated to each other and, thereafter, a space definedbetween the element substrate and the sealing substrate is filled withsilicone oil. Since silicone oil works as a stress buffering material,the substrate is hardly broken even when the substrate is curved orwarped by an external force.

However, even when silicone oil is dehydrated for a long time, it isdifficult to dehydrate silicone oil to an extent that silicone oil ispractically applicable to an organic EL display device and hence, with alapse of time, moisture in silicone oil precipitates and intrudes intoan organic EL layer thus lowering a lifetime of the element.

JP-A-2005-533319 discloses another related art of the solid sealingstructure. To before specific, a desiccant is supplied in a state wherethe desiccant is dissolved in an adhesive organic solvent, and achemical reaction is generated by heat or light thus making an elementsubstrate and a sealing substrate adhered to each other.

The technique disclosed in patent document 1 has following drawbacks.That is, the technique uses a liquid as a desiccant and hence, thetechnique requires the structure for injecting the liquid in the insideof the organic EL display device. Further, the technique requires aliquid injecting process and hence, manufacturing steps becomecomplicated.

On the other hand, the technique disclosed in patent document 2 hasfollowing drawbacks. That is, when the desiccant is supplied in a solstate where the desiccant is impregnated in a low-molecular organicsolution used as an adhesive material, an organic solvent is vigorouslyevaporated. The vigorous evaporation of the organic solvent implies thatan adhesive strength is strong. The rapid evaporation, on the otherhand, implies that an organic gas is liable to remain in the organicsolvent correspondingly. This organic gas, as a result, shortens alifetime of the organic EL display device. Accordingly, in the relatedart, it is necessary to form a silicon nitride film having a largethickness as a background film of a desiccant containing adhesivematerial. Further, there also exists a drawback that the solvent havinglow viscosity such as a solvent in a sol state is difficult to handle.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, there is provided anorganic EL display device which includes: a first substrate on whichorganic EL layers are formed in a matrix array; a second substrate whichfaces the first substrate in an opposed manner; and a sealing materialwhich is formed in an annular shape between inner peripheries of thefirst substrate and the second substrate, wherein a gel which is formedby mixing a desiccant in a medium having a molecular weight of not lessthan 1,000 is filled in a space defined inside the sealing material.

According to another aspect of the present invention, there is providedan organic EL display device which includes: a first substrate on whichpixels each of which has an organic EL layer sandwiched between an upperelectrode and a lower electrode are formed in a matrix array; a secondsubstrate which is arranged to face the first substrate in an opposedmanner; and a sealing material which is formed in an annular shapebetween inner peripheries of the first substrate and the secondsubstrate, wherein a protective film is formed above the upperelectrode, and a gel which is formed by mixing a desiccant into a mediumhaving a molecular weight of not less than 1,000 is filled in a spacedefined between the protective film formed on the first substrate andthe second substrate and inside the sealing material.

According to still another aspect of the present invention, there isprovided a manufacturing method of an organic EL display device whichincludes a first substrate on which organic EL layers are formed in amatrix array, a second substrate which faces the first substrate in anopposed manner, and a sealing material which is formed in an annularshape between inner peripheries of the first substrate and the secondsubstrate, wherein the manufacturing method of an organic EL displaydevice includes: a first step of forming a sealing material made of anultraviolet-ray curing resin in an annular shape on the periphery of thesecond substrate, and forming a half-cured sealing material by radiatingultraviolet rays to the sealing material; a second step of arranging agel-state desiccant inside the half-cured sealing material; a third stepof adhering the first substrate and the second substrate, and filling aregion surrounded by the first substrate, the second substrate and thesealing material with the gel-state desiccant; and a fourth step offorming the half-cured sealing material into a completely cured sealingmaterial.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a display region of an organic ELdisplay device of an embodiment 1 according to the present invention;

FIG. 2A to FIG. 2D are views showing steps of a sealing-substrate-sideprocess in a manufacturing method of the organic EL display device ofthe embodiment 1 according to the present invention;

FIG. 3A to FIG. 3C are views showing steps which follow themanufacturing step shown in FIG. 2D in the embodiment 1, wherein FIG. 3Ashows the manufacturing step performed in a reduced pressure atmosphere,FIG. 3B shows the manufacturing step performed in anatmospheric-pressure atmosphere, and FIG. 3C shows the manufacturingstep for curing a sealing material;

FIG. 4 is a schematic cross-sectional view of the organic EL displaydevice of the embodiment 1;

FIG. 5 is a cross-sectional view of a display region of an organic ELdisplay device of an embodiment 2;

FIG. 6A to FIG. 6C are views showing steps of the embodiment 2, where inFIG. 6A shows the manufacturing step performed in a reduced pressureatmosphere, FIG. 6B shows the manufacturing step performed in anatmospheric-pressure atmosphere, and FIG. 6C shows the manufacturingstep for curing a sealing material; and

FIG. 7 is a schematic cross-sectional view of the organic EL displaydevice of the embodiment 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT

To explain the specific constitutions of the present invention toovercome the above-mentioned drawbacks, they are as follows.

(1) In an organic EL display device which includes: a first substrate onwhich organic EL layers are formed in a matrix array; and a secondsubstrate which faces the first substrate in an opposed manner, asealing material is formed in an annular shape on the peripheries ofoppositely-facing surfaces of the first substrate and the secondsubstrate. A gel which is formed by mixing a desiccant in a mediumhaving a molecular weight of not less than 1,000 is filled in a spacesurrounded by the first substrate, the second substrate and the sealingmaterial.

(2) In the organic EL display device having the constitution (1), themedium has a molecular weight of not less than 1,000 and not more than10,000.

(3) In the organic EL display device having the constitution (1), thesealing material is made of an ultraviolet-ray curing.

(4) In an organic EL display device which includes: a first substrate onwhich pixels each of which has an organic EL layer sandwiched between anupper electrode and a lower electrode are formed in a matrix array; anda second substrate which is arranged to face the first substrate in anopposed manner; wherein a sealing material is formed in an annular shapeon the peripheries of oppositely-facing surfaces of the first substrateand the second substrate. A protective film is formed above the upperelectrode. Further, a gel which is formed by mixing a desiccant into amedium having a molecular weight of not less than 1,000 is filled in aspace surrounded by the protective film formed on the first substrate,the second substrate and the sealing material.

(5) In the organic EL display device having the constitution (4), themedium has a molecular weight of not less than 1,000 and not more than10,000.

(6) In the organic EL display device having the constitution (4), theprotective film is formed of an SiN film.

(7) In a manufacturing method of an organic EL display device whichincludes a first substrate on which organic EL layers are formed in amatrix array, a second substrate which faces the first substrate in anopposed manner, and a sealing material which is formed in an annularshape between inner peripheries of the first substrate and the secondsubstrate, the manufacturing method of an organic EL display deviceincludes: a first step of forming a sealing material made of anultraviolet-ray curing resin in an annular shape on the periphery of thesecond substrate, and forming a half-cured sealing material by radiatingultraviolet rays to the sealing material; a second step of arranging agel-state desiccant inside the half-cured sealing material; a third stepof adhering the first substrate and the second substrate, and filling aregion surrounded by the first substrate, the second substrate and thesealing material with the gel-state desiccant; and a fourth step offorming the half-cured sealing material into a completely cured sealingmaterial.

(8) In the manufacturing method of an organic EL display device havingthe constitution (7), in the third step, the first substrate and thesecond substrate are laminated to each other in a reduced pressureatmosphere, and the gel-state desiccant is filled in the regionsurrounded by the first substrate, the second substrate and the sealingmaterial in an atmospheric-pressure atmosphere.

(9) In the manufacturing method of an organic EL display device, havingthe constitution (7), the first to the third steps are performed in anitrogen atmosphere.

According to the present invention, the gel-state desiccant is filled inthe space defined between the element substrate and the sealingsubstrate and hence, it is possible to increase a mechanical strength ofthe organic EL display device. Further, even when a force is applied tothe element substrate of the sealing substrate from the outside, thereis no possibility that the organic EL layer is brought into contact withthe sealing substrate and hence, it is possible to prevent thegeneration of dark spots attributed to contacting of the organic ELlayer with the scaling substrate.

Further, the space defined between the element substrate and the sealingsubstrate is filled with the gel-state desiccant and hence, moisturehardly intrudes into the space from the outside. Further, even whenmoisture intrudes into the space from the outside, the moisture isabsorbed by the gel-state desiccant and hence, it is possible to prolonga lifetime of the organic EL display device.

Further, since the gel-state desiccant used in the present invention isin a gel state, if is possible to prevent the occurrence of coatingmottles or non-uniform drying which is observed when a transparentdesiccant is applied by coating.

Further, the gel-state desiccant is used in the present invention, it isunnecessary to form a recessed portion for placing a desiccant in thesealing substrate and hence, it is possible to realize the reduction ina manufacturing cost of the sealing substrate leading to the reductionin a manufacturing cost of the organic EL display device.

Hereinafter, the present invention is explained in detail in conjunctionwith embodiments.

Embodiment 1

FIG. 1 is a cross-sectional view of a display region of atop-emission-type organic EL display device to which the presentinvention is applied. Although this embodiment is explained by takingthe top-emission-type organic EL display device as an example, thepresent invention is also applicable to a bottom-emission type organicEL display device in the same manner. The top-emission-type organic ELdisplay device can be classified into a top-anode-type organic ELdisplay device in which an anode is arranged above an organic EL layer22 and a top-cathode-type organic EL display device in which a cathodeis arranged above an organic EL layer 22. Although FIG. 1 shows thetop-anode type organic EL display device, the present invention is alsoapplicable to the top-cathode type organic EL display device in the samemanner.

As shown in FIG. 1, a first background film 11 made of SiN and a secondbackground film 12 made of SiO₂ are formed on an element substrate 10.These background films 11, 12 are provided for preventing impuritiesfrom a glass substrate from contaminating a semiconductor layer 13. Thesemiconductor layer 13 is formed on the second background film 12. Informing the semi-conductor layer 13, an a-Si film is firstly formed by aCVD method and, thereafter, the a-Si film is transformed into a poly-Sifilm by radiating laser beams to the a-Si film.

A gate insulation film 14 made of SiO₂ is formed so as to cover thesemiconductor layer 13. A gate electrode 15 is formed in a state thatthe gate electrode 15 faces the semiconductor layer 13 in an opposedmanner with the gate insulation film 14 sandwiched therebetween. Usingthe gate electrode 15 as a mask, the semiconductor layer 13 is dopedwith impurities such as phosphorus or boron by ion implantation so as tomake the semiconductor layer 13 conductive thus forming a source portionor a drain portion in the semiconductor layer 13.

An interlayer insulation film 16 made of SiO₂ is formed so as to coverthe gate electrode 15. The inter layer insulation film 16 is providedfor ensuring the insulation between gate lines and drain lines 171. Thedrain line 171 is formed on the interlayer insulation film 16. The drainline 171 is connected with the drain of the semiconductor layer 13 via athrough hole formed in the interlayer insulation film 16 and the gateinsulation film 14. Here, since the organic EL display device uses thinfilm transistors, as a matter of course, the structure shown in FIG. 1requires a source electrode. However, the source electrode is not shownin FIG. 1.

Thereafter, to protect a thin film transistor (TFT) formed in theabove-mentioned manner, an inorganic passivation film 18 made of SiN isformed on the interlayer insulation film 16, the thin film transistorsand the drain lines 171 by coating. An organic passivation film 19 isformed on the inorganic passivation film 18. The organic passivationfilm 15 plays a role of protecting the TFT more completely together withthe inorganic passivation film 18. The organic passivation film 19 alsoplays a role of leveling a surface on which an organic EL layer 22 isformed. Accordingly, the organic passivation film 19 is formed with alarge thickness of 1 to 4 μm.

A reflection electrode made of Al or Al alloy is formed on the organicpassivation film 13. Since Al or Al alloy exhibits high reflectance, Alor Al alloy is preferably used as a material of the reflectionelectrode. The reflection electrode is connected with the drain line 171via a through hole formed in the organic passivation film 19 and theinorganic passivation film 18.

This embodiment provides the top-anode-type organic EL display deviceand hence, a lower electrode 21 of the organic EL layer 22 constitutes acathode. Accordingly, the Al layer or Al alloy layer which is used forforming the reflection electrode is also used for forming the lowerelectrode 21 of the organic EL layer 22. This is because Al or Al alloypossesses a relatively small work function and hence, Al or Al alloy canfunction as cathodes.

The organic EL layer 22 is formed on the lower electrode 21. The organicEL layer 22 is constituted of an electron transport layer, a lightemission layer and a hole transport layer which are laminated frombelow. Here, an electron injection layer may be interposed between theelectron transport layer and the lower electrode 21. Further, a holeinjection layer may be interposed between the hole transport layer andan upper electrode 23. The upper electrode 23 which constitutes an anodeis formed on the organic EL layer 22. In this embodiment, the upperelectrode 23 is made of IZO. The IZO film is formed over the wholedisplay region by vapor deposition without using a mask. A thickness ofthe IZO film is set to approximately 30 nm for maintaining opticaltransmissivity. An ITO film may be used in place of the IZO film.

A material which can be used as an electron-transport-layer material isnot specifically limited provided that the material exhibits electrontransport property and can be easily formed into a charge-transfercomplex by co-deposition with alkali metal and, for example, a metalcomplex such as tris (8-quinolinolato) aluminum, tris(4-methyl-8-quinolinolato) aluminum, bis(2-methyl-8-quinolinolato)-4-phenylphenolato-aluminum, bis[2-[2-hydroxyphenyl]benzooxazolato]zinc,2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazol, 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene or the like can beused.

A material which can be used as a light-emitting-layer material is notspecifically limited provided that the material is made of a hostmaterial having an electron-and-hole transporting ability to which adopant which emits a fluorescent light or a phosphorus light byre-coupling thereof is added and the material forms a light emittinglayer by co-vapor-deposition. For example, as the host material, acomplex such as tris (8-quinolinolato) aluminum, bis (8-quinolinolato)magnesium, bis (benzo{f}-8-quinolinolato) zinc, bis(2-methyl-8-quinolinolato) aluminum oxide, tris (8-quinolinolato)indium, tris (5-methyl-8-quinolinolato) aluminum, 8-quinolinolatolithium, tris (5-chloro-8-quinolinolato) gallium, bis(5-chloro-8-quinolinolato) calcium, 5,7-dichloro-8-quinolinolatoaluminum, tris (5,7-dibromo-8-hydroxyquinolinolato) aluminum, and poly[zinc(II)-bis(8-hydroxy-5-quinolinyl) methane], an anthracenederivative, a carbazole derivative, or the like can be used.

Further, the dopant may be a material which captures electrons and holesin a host material and emits light by re-coupling. For example, the reddopant may be formed of a pyran derivative, the green dopant may beformed of a coumarin derivative, and the blue dopant may be formed of asubstance which emits fluorescent light such as an anthracene derivativeor a substance which emits phosphorescence such as an iridium complexand a pyridinato derivative.

The hole transport layer may be made of, for example, a tetraarylbenzidine compound (triphenyl diamine: TPD), aromatic tertiary amine, ahydrazone derivative, a carbazole derivative, a triazole derivative, animidazole derivative, an oxadiazole derivative having an amino group, apolythiophene derivative, a copper phthalocyanine derivative or thelike.

Here, to prevent the organic EL layer 22 from being broken at an edgeportion thereof due to a broken step, a bank 20 is formed between thepixels. The bank 26 may be formed of an organic material, or the bank 20may be formed of an inorganic material such as SiN. In forming the bank20 using the organic material, in general, an acrylic resin is used.

An auxiliary electrode may be formed on the upper electrode which isformed on the bank 20 for assisting the electrical conduction of theupper electrode. This is because when the resistance of the upperelectrode is large, brightness irregularities may occur. Although theauxiliary electrode is not used in this embodiment, it is needless tosay that the present invention is also applicable to an organic ELdisplay device which uses the auxiliary electrode.

In FIG. 1, a gel-state desiccant 30 for protecting the organic EL layerfrom moisture is sandwiched between the upper electrode of the elementsubstrate 10 and the sealing substrate 40. In the present invention, thegel-state desiccant 30 is used as a desiccant. The gel-state desiccant30 is formed by dispersing a desiccant in a gel-state material. Thegel-state desiccant 30 is flexibly deformed when a force is applied fromthe outside while keeping a solid state. According to the presentinvention, by making use of the flexibility of the gel-state desiccant30, the desiccant is uniformly filled up in a apace defined between theelement substrate 10 and the sealing substrate 40 without forming a gap.As a gel-state material for forming the gel-state desiccant 30, a resinwhich is referred to as dendrimer whose molecular weight is not lessthan 1000 and not more than 10000 can be suitably used. As the desiccantwhich is dispersed in the gel-state material, silica gel, alcoholate orthe like can be used. The sealing substrate 40 which sandwiches thegel-state desiccant 30 with the element substrate 10 is formed of aglass sheet, and the glass sheet has a thickness of approximately 0.5mm.

FIG. 2A, FIG. 2B, FIG. 2C and FIG. 2D are views showing steps of asealing-substrate-40-side process in a manufacturing method of theorganic EL display device according to the present invention. FIG. 2Ashows the sealing substrate 40 which is formed of a glass sheet. Thesealing substrate 40 is formed of a flat glass sheet. In a related art,in placing the desiccant on the sealing substrate 40, a recessed portionis formed in a portion of the sealing substrate 40 on which thedesiccant is placed by sand blasting or the like. However, since thepresent invention uses the gel-state desiccant 30, it is unnecessary toform such a recessed portion in the sealing glass substrate. This isbecause a sealing material formed on the periphery of the sealingsubstrate 40 works as a stopper for the gel-state desiccant 30 asdescribed below.

To the periphery of the sealing substrate 40, a sealing material 50 isapplied by coating using a dispenser. The sealing material 50 is formedin a loop shape with no opening portion. The sealing material 50 is madeof an ultraviolet-ray curing resin. Coating of the sealing material 50using the dispenser is performed in a nitrogen atmosphere.

The sealing material 50 applied to the periphery of the sealingsubstrate 40 by coating using the dispenser has fluidity although theviscosity of the sealing substrate 50 is high. Accordingly, as shown inFIG. 2B, ultraviolet rays are radiated to the sealing material 50 whichis formed on the periphery of the sealing substrate 40 to form ahalf-cured sealing material 51. In a stage which comes later, thesealing substrate 40 and the element substrate 10 are adhered to eachother and, thereafter, the sealing material 50 is formed into acompletely-cured sealing material 52. Accordingly, at this paint oftime, the sealing material 50 is held as the half-cured sealing material51.

Thereafter, as shown in FIG. 2C, the gel-state desiccant 30 is droppedin a space defined inside the half-cured sealing material 51 which isformed in a loop shape. Usually, the gel-state desiccant 30 is droppedin a gel state. However, when it is difficult to drop the gel-statedesiccant 30 because of viscosity of the gel-state desiccant 30, thegel-state desiccant 30 may be applied by coating in a state where thegel-state desiccant 30 is dissolved in a low molecular solvent. Also inthis case, the half-cured sealing material 51 formed on the periphery ofthe sealing substrate 40 becomes a stopper for the low molecular solventin which the gel-state desiccant 30 is dissolved. When the gel-statedesiccant 30 is made of dendrimer and the dendrimer has a chemicalpolarity, the dendrimer can be easily dissolved in the low molecularsolvent and hence, dendrimer can be easily dropped into the spacedefined inside the half-cured sealing material 51. Here, the chemicalpolarity implies that, when the molecular structure has the chainstructure, the molecular structure differs between a left end and aright end thereof.

When a required amount of the solvent in which the gel-state desiccant30 is dissolved is dropped in the space defined inside the half-curedsealing material 51, the low molecular solvent in the solvent isimmediately evaporated and the applied solvent returns to a state of thegel-state desiccant 30. The evaporation of the low molecular solvent isso fast that the low molecular solvent is dissipated before a step ofadhering the sealing substrate 40 and the element substrate 10 to eachother.

FIG. 2D shows a state where the gel-state desiccant 30 is applied to thesealing substrate 40 in the above-mentioned manner. As shorn in FIG. 2D,the gel-state desiccant 30 is in a gel state and hence, the gel-statedesiccant 30 does not assume a fixed solid state even after thegel-state desiccant 30 is applied to the sealing substrate 40 bycoating, and an upper surface of the gel-state desiccant 30 is notflattened and, for example, forms a gentle mount. Here, all steps shownin FIG. 2A to FIG. 2D are performed in a nitrogen atmosphere.

As shown in FIG. 2D, although the sealing substrate 40 to which thegel-state desiccant 30 is applied by coating is in the nitrogenatmosphere, by reducing the pressure in the atmosphere, air bubbles 60or the like contained in the gel-state desiccant 30 are removed. At thispoint of time, the low molecular solvent which is not removed heretoforeis completely removed.

To the sealing substrate 40 from which the bubbles are removed in theabove-mentioned manner, the element substrate 10 is adhered. Theadhering operation is also performed in the reduced-pressure atmosphere.This state is shown in FIG. 3A. In FIG. 3A, to prevent the drawing frombecoming complicated, only the organic EL layer is described on theelement substrate 10. In the state shown in FIG. 3A, the sealingsubstrate 40 and the element substrate 10 are merely adhered to eachother. Accordingly, the bubbles 60 or the like are present between thegel-state desiccant 30 in the space defined inside the half-curedsealing material 51 and the element substrate 10.

Thereafter, nitrogen is supplied to the ambient atmosphere in which thesealing substrate 40 and the element substrate 10 are adhered to eachother so as to return the pressure of the ambient atmosphere to anatmospheric pressure. In this manner, the element substrate 10 and thesealing substrate 40 are pushed by the atmospheric pressure and hence,the bubbles 60 which are present between the sealing substrate 40 andthe element substrate 10 are eliminated or dissipated. Further, sincethe element substrate 10 and the sealing substrate 40 are pushed fromabove and below, the half-cured sealing material 51 also collapses andis deformed into a shape which provides the more reliable sealingbetween the element substrate 10 and the sealing substrate 40. Thisstate is shown in FIG. 3B.

In FIG. 3B, the inner space surrounded by the element substrate 10, thesealing substrate 40 and the half-cured sealing material 51 is filled upwith the gel-state desiccant 30 without forming a gap and hence, no airbubbles 60 or the like are present in the inner space. That is, sincethe gel-state desiccant 30 is in a gel state, the gel-state desiccant 30is not completely solid and hence, the gel-state desiccant 30 can beflexibly filled in the gap. Further, various layers are formed on theelement substrate 10 so that a surface of the element substrate 10becomes uneven when viewed microscopically. However, the gel-statedesiccant 30 can flexibly conform to such an uneven surface and isfilled in the concave portions of the uneven surface.

In a state shown in FIG. 3B, the half-cured sealing material 51 is hotin a completely cured state and hence, the adhesion between the elementsubstrate 10 and the sealing substrate 40, the sealing reliability andthe like are not sufficiently ensured. Accordingly, as shown in FIG. 3C,ultraviolet rays are radiated to the sealing material 50 so as to bringthe sealing material 50 into a cured sealing material 52 which iscompletely cured. Here, the cured sealing material 52 may be cured to anextent that the cured sealing material 52 can adhere the sealingsubstrate 40 and the element substrate 10 to each other and the adhesionis maintained with reliability. On the other hand, when ultraviolet raysare radiated to the organic EL layers, the organic EL layers are broken.Accordingly, in FIG. 3C, an ultraviolet-ray cover 70 is arranged on aportion of the element substrate 10 where the organic EL layers areformed thus allowing ultraviolet rays to be radiated only to the sealingmaterial 50 portion.

Here, in FIG. 3C, ultraviolet rays are radiated to the half-curedsealing material 51 so as to form the half-cured sealing material 51into the cured sealing material 52. However, in forming the half-curedsealing material 51 into the cured sealing material 52, depending on amaterial to be used for forming the sealing material, besides theradiation of ultraviolet-rays, the half-cured sealing material 51 may beformed into the cured sealing material 52 also by heating. In this case,it is necessary to set a heating temperature to a value which fallswithin a range which does not cause breaking of the organic EL layers.

While FIG. 3C shows a state where the sealing portion is formed of thecured sealing material 52 by radiating ultraviolet rays, FIG. 4 shows astate of a next step where the ultraviolet-ray cover 70 is removed. Thatis, FIG. 4 is a schematic cross-sectional view showing a state of theorganic EL display device of this embodiment in a completed state. InFIG. 4, light emitted from the organic EL layers is radiated toward thesealing substrate 40 side, that is, in the direction indicated by anarrow L shown in FIG. 4. The gel-state desiccant 30 which is filledbetween the element substrate 10 and the sealing substrate 40 isflexibly filled in a boundary portion between the gel-state desiccant 30and the sealing substrate 40 and hence, even when the light passes thegel-state desiccant 30 and is taken out from the sealing substrate 40side, the gel-state desiccant 30 does not hamper the formation of animage.

As shown in FIG. 4, surfaces of the organic EL layers are completelycovered with the gel-state desiccant 30. Further, the space definedbetween the element substrate 10 and the sealing substrate 40 is filledwith the gel-state desiccant 30 and hence, a mechanical strength of theorganic EL display device is enhanced. Accordingly, even when a force isapplied to the element substrate 10 or the sealing substrate 40 from theoutside, the gel-state desiccant 30 can prevent the organic EL layer andthe sealing substrate 40 from being brought into contact with eachother.

Further, according to the constitution of the present invention, thegel-state desiccant 30 is filled in the space defined between theelement substrate 10 and the sealing substrate 40 and hence, differentfrom the constitution of a hollow-sealed-type organic EL display device,moisture hardly intrudes into the inside of the organic EL displaydevice from the outside. Still further, even when moisture intrudes intothe inside of the organic EL display device from the outside, moistureis absorbed by the gel-state desiccant 30 and hence, the organic ELdisplay device of the present invention can enjoy a long lifetime.

Further, the gel-state desiccant 30 of the present invention is in a gelstate and hence, compared to a conventional case in which a desiccant isapplied by coating, coating mottles or non-uniform drying hardly occurs.

Further, according to the present invention, the gel-state desiccant 30is placed on the sealing substrate 40 using the sealing material 50 as astopper. On the other hand, in a related art, in placing a soliddesiccant on the sealing substrate 40, a recessed portion is formed inthe sealing substrate 40 and a desiccant is placed in the recessedportion. Accordingly, in the related art, it is necessary to form therecessed portion in the sealing substrate 40 by sand blasting or thelike and hence, a manufacturing cost of the sealing substrate 40 ispushed up. According to the present invention, a flat plate may be usedfor forming the sealing substrate 40 and hence, the increase inmanufacturing costs of the sealing substrate 40 can be suppressed.

Heretofore, the explanation has been made with respect to the case inwhich the single organic EL display device is manufacturedindependently. However, in the actual manufacture of the organic ELdisplay devices, from a viewpoint of enhancement of manufacturingefficiency, the organic EL display devices are manufactured as follows.A large mother element substrate on which a plurality of elementsubstrates 10 is formed and a large mother sealing substrate on which aplurality of sealing substrates 40 is formed are laminated to each otherso as to form a plurality of organic EL display devices. Thereafter, thelaminated structure is divided into individual organic EL displaydevices. The present invention is also applicable to the organic ELdisplay devices which are manufactured by such a manufacturing process.

Embodiment 2

FIG. 5 is a cross-sectional view of a display part of an organic ELdisplay device according to an embodiment 2 of the present invention. InFIG. 5, the structure up to the upper electrode from the elementsubstrate 10 of this embodiment is equal to the corresponding structureshown in FIG. 1. In the structure shown in FIG. 5, a protective film 24is formed on the upper electrode. The gel-state desiccant 30 protectsthe organic EL layer by absorbing moisture intruded from the outside.However, it is desirable that even when the moisture-absorbing propertyof the gel-state desiccant 30 becomes insufficient, such a state doesnot cause an immediate malfunction of the organic EL display device andthe organic EL display device continues an operation thereof for apredetermined time.

In this embodiment, by forming the protective film 24 which prevents theintrusion of moisture on a surface of the upper electrode, even when themoisture absorbing property of the gel-state desiccant 30 becomesinsufficient, the organic EL display device can perform an operationthereof for a predetermined time. Due to such constitution, the organicEL display device can ensure a more prolonged lifetime than the organicEL display device of the embodiment 1.

The protective film 24 is formed of an SiN film. Although the protectivefilm 24 is formed of an SiN_(x) film in many cases in the actualmanufacture of the organic EL display device, the protective film 24 isformed of the SiN film as a representative example. The SiN film may beformed by various methods. In this embodiment, the protective film 24 isformed after the formation of the organic EL layer. Since the organic ELlayer is broken at a high temperature, it is impossible to form the SiNfilm at a high temperature. In this embodiment, the SiN film is formedby a low-temperature CVD method. In the low-temperature CVD method, afilm can be formed at a temperature of not more than 200° C. Further, inthis case, temperature of the element substrate 10 can be held at atemperature of approximately 80° C.

In FIG. 5, the gel-state desiccant 30 is sandwiched between theprotective film 24 of the element substrate 10 and the sealing substrate40. In the embodiment shown in FIG. 5, the organic EL display device is,in the same manner as the embodiment 1, a top-emission-type organic ELdisplay device in which light from the organic EL layer is radiated inthe direction indicated by an arrow L shown in FIG. 5.

A manufacturing method of the sealing substrate 40 used in thisembodiment is substantially equal to the manufacturing method shown inFIG. 2 which is explained in conjunction with the embodiment 1. Thewhole process shown in FIG. 2 is performed in a nitrogen atmosphere.

To the sealing substrate 40 which is formed by the process shown in FIG.2, the element substrate 10 which is formed separately from the sealingsubstrate 40 is laminated. The laminated structure constituted of thesealing substrate 40 and the element substrate 10 is shown in FIG. 6A.The process shown in FIG. 6A is equal to the process of the embodiment 1shown in FIG. 3A except for that the protective film 24 is formed on theelement substrate 10. The process shown in FIG. 6A is performed in apressure-reduced nitrogen atmosphere.

FIG. 6B is a view which shows steps in which nitrogen is supplied to theambient atmosphere in which the sealing substrate 40 is laminated to theelement substrate 10 in a pressure-reduced state shown in FIG. 6A, andan atmospheric pressure is applied to the element substrate 10 and thesealing substrate 40 so as to eliminate bubbles 60 or the like in theinside of the laminated structure. The process shown in FIG. 6B issubstantially equal to the process of the embodiment 1 shown in FIG. 3B.

Thereafter, ultraviolet rays are radiated to the half-cured sealingmaterial 51 so as to make the adhesion between the element substrate 10and the sealing substrate 40 complete and, at the same time, to enhancethe sealing property. This process is also substantially equal to theprocess of the embodiment 1 shown in FIG. 3C.

Further, in FIG. 6C, ultraviolet rays are radiated to the half-curedsealing material 51 so as to form the half-cured sealing material 51into the cured sealing material 52 which is completely cured. However,in forming the half-cured sealing material 51 into the cured sealingmaterial 52, depending on a material to be used for forming the sealingmaterial, besides the radiation of ultraviolet rays, the half-curedsealing material 51 may be formed into the cured sealing material 52also by heating. In this case, it is necessary to set a heatingtemperature to a value which falls within a range which does not causebreaking of the organic EL layers.

FIG. 7 is a cross-sectional view of the organic EL display device of theembodiment 2 which is completed by removing the ultraviolet-ray cover70. In FIG. 7, the light emitted from the organic EL layers is radiatedin the direction indicated by an arrow L. The constitution shown in FIG.7 is substantially equal to the constitution shown in FIG. 4 which is across-sectional view of the embodiment 1 except for that the protectivefilm 24 is formed on surfaces of the organic EL layers. In FIG. 7, thegel-state desiccant 30 is filled in the space defined between theprotective film 24 of the element substrate 10 and the sealing substrate40 without forming a gap. Accordingly, even when an external force isapplied to the sealing substrate 40 or the element substrate 10, it ispossible to prevent the organic EL layer and the sealing substrate 40from being brought into contact with each other.

Further, also in this embodiment, the gel-state desiccant 30 is filledin the space defined between the sealing substrata 40 and the elementsubstrate 10 and hence, the organic EL display device of this embodimentcan also acquire various advantageous effects including the followingadvantageous effects in the same manner as the embodiment 1. That is,moisture hardly intrudes into the inside of the organic EL displaydevice from the outside. A mechanical strength of the organic EL displaydevice can be enhanced. It is unnecessary to form a recessed portion orthe like in the sealing substrate 40 and hence, a flat plate can be usedfor forming the sealing substrate 40.

In FIG. 7, the organic EL layer is covered with the protective film 24.Accordingly, even when the moisture absorbing property of the gel-statedesiccant 30 is lowered, the organic EL display device of thisembodiment can be operated for a considerably long time and hence, lifecharacteristics of the organic EL display device can be enhanced.Further, the protective film 24 can block moisture which intrudes alongan interface between the gel-state desiccant 30 and the elementsubstrate 10. Also due to such constitution, the organic EL displaydevice of this embodiment can exhibit excellent life characteristics.

In FIG. 7, the explanation has been made with respect to the case inwhich the protective film 24 is formed of the single-layered SiN film.However, the protective film 24 of this embodiment is not necessarilylimited to such single-layered structure and the protective film 24 maybe formed of a plurality of films. The protective film 24 is made of SiNin this embodiment. However, a material of the protective film is notlimited to SiN and the protective film 24 may be made of SiO₂ or thelike. Further, the protective film 24 may be formed of a combination ofah SiN film and an SiO₂ film.

Heretofore, the explanation has been made with respect to the case inwhich the single organic EL display device is manufacturedindependently. However, in the actual manufacture of the organic ELdisplay devices, from a viewpoint of enhancement of manufacturingefficiency, the organic EL display devices are manufactured as follows.A large mother element substrate on which a plurality of elementsubstrates 10 is formed and a large mother sealing substrate on which aplurality of sealing substrates 40 is formed are laminated to each otherso as to form a plurality of organic EL display devices. Thereafter, thelaminated structure is divided into individual organic EL displaydevices. This embodiment is also applicable to the organic EL displaydevices which are manufactured by such a manufacturing process in thesame manner as the embodiment 1.

What is claimed is:
 1. An organic EL display device comprising: a firstsubstrate having a display region which includes a plurality of pixelsand a peripheral region which surrounds the display region, each of theplurality of pixels having a pixel electrode and an organic EL layerformed on the pixel electrode; a second substrate facing the firstsubstrate; an upper electrode formed on the organic EL layer; a resinsandwiched between the first substrate and the second substrate; and aprotective film is formed of inorganic material and covering the upperelectrode, wherein the protective film over the peripheral region isbeing thinner than the protective film over the display region, and theupper electrode is in direct contact with the protective film.
 2. Theorganic EL display device according to claim 1, wherein the protectivefilm is formed of a plurality of inorganic layers.
 3. The organic ELdisplay device according to claim 2, wherein at least one of theplurality of inorganic layers is formed of silicon nitride.
 4. Theorganic EL display device according to claim 2, wherein at least one ofthe plurality of inorganic layers is formed of silicon oxide.
 5. Theorganic EL display device according to claim 1, wherein the resin issandwiched between the second substrate and the protective film coveringthe peripheral region and the display region.
 6. The organic EL displaydevice according to claim 1, wherein the upper electrode is formed overthe whole display region.
 7. The organic EL display device according toclaim 6, the upper electrode is made of IZO or ITO.
 8. An organic ELdisplay device comprising: a first substrate having a display regionwhich includes a plurality of pixels and a peripheral region whichsurrounds the display region, each of the plurality of pixels having apixel electrode, and an organic EL layer formed on the pixel electrode;a second substrate facing the first substrate; an upper electrode formedon the organic EL layer; a resin sandwiched between the first substrateand the second substrate; and a protective film having more than twoinorganic layers and covering the upper electrode, wherein a totalthickness of the more than two inorganic layers over the peripheralregion is thinner than a total thickness of the more than two inorganiclayers over the display region, and the upper electrode is in directcontact with the protective film.
 9. The organic EL display deviceaccording to claim 8, wherein at least one of the more than twoinorganic layers is formed of silicon nitride.
 10. The organic ELdisplay device according to claim 8, wherein at least one of the morethan two inorganic layers is formed of silicon oxide.
 11. The organic ELdisplay device according to claim 8, wherein the resin is sandwichedbetween the second substrate and the protective film covering theperipheral region and the display region.
 12. The organic EL displaydevice according to claim 8, wherein the upper electrode is formed overthe whole display region.
 13. The organic EL display device according,to claim 12, the upper electrode is made of IZO or ITO.
 14. An organicEL display device comprising: a first substrate having a display regionwhich includes a plurality of pixels and a peripheral region whichsurrounds the display region, each of the plurality of pixels having apixel electrode, and an organic EL layer formed on the pixel electrode;a second substrate facing the first substrate; and an upper electrodeformed on the organic EL layer; a resin sandwiched between the firstsubstrate and the second substrate; and an inorganic film having morethan two inorganic layers and covering the upper electrode, wherein theinorganic film over the peripheral region is thinner than the inorganicfilm over the display region, and the upper electrode is in directcontact, with the inorganic film.
 15. The organic EL display deviceaccording to claim 14, wherein at least one of the more than twoinorganic layers is formed of silicon nitride.
 16. The organic ELdisplay device according to claim 14, wherein at least one of the morethan two inorganic layers is formed of silicon oxide.
 17. The organic ELdisplay device according, to claim 14, wherein the resin is sandwichedbetween the second substrate and the inorganic film covering theperipheral region and the display region.
 18. The organic EL displaydevice according to claim 14, wherein the upper electrode is formed overthe whole display region.
 19. The organic EL display device according toclaim 18, the upper electrode is made of IZO or ITO.